Ethionine Fatty Liver12 1The author's research work included in this review was supported by funds from the National Cancer Institute, National Institute of Arthritis and Metabolic Diseases and National Institute of General Medical Sciences, U. S. Public Health Service, the American Cancer Society, the Life Insurance Medical Research Fund, and the Beaver County Cancer Society. 2The invaluable assistance of Mrs. Virginia Newman is gratefully acknowledged

Analysis of time-related metabolic fluctuations induced by ethionine in the rat

The time-course of metabolic events following response to a model hepatotoxin ethionine (800 mg/kg) was investigated over a 7 day period in rats using high-resolution (1)H NMR spectroscopic analysis of urine and multivariate statistics. Complementary information was obtained by multivariate analysis of (1)H MAS NMR spectra of intact liver and by conventional histopathology and clinical chemistry of blood plasma. (1)H MAS NMR spectra of liver showed toxin-induced lipidosis 24 h postdose consistent with the steatosis observed by histopathology, while hypertaurinuria was suggestive of liver injury. Early biochemical changes in urine included elevation of guanidinoacetate, suggesting impaired methylation reactions. Urinary increases in 5-oxoproline and glycine suggested disruption of the gamma-glutamyl cycle. Signs of ATP depletion together with impairment of the energy metabolism were given from the decreased levels in tricarboxylic acid cycle intermediates, the appearance of ketone bodies in urine, the depletion of hepatic glucose and glycogen, and also hypoglycemia. The observed increase in nicotinuric acid in urine could be an indication of an increase in NAD catabolism, a possible consequence of ATP depletion. Effects on the gut microbiota were suggested by the observed urinary reductions in the microbial metabolites 3-/4-hydroxyphenyl propionic acid, dimethylamine, and tryptamine. At later stages of toxicity, there was evidence of kidney damage, as indicated by the tubular damage observed by histopathology, supported by increased urinary excretion of lactic acid, amino acids, and glucose. These studies have given new insights into mechanisms of ethionine-induced toxicity and show the value of multisystem level data integration in the understanding of experimental models of toxicity or disease.

Therapeutic treatment with poly(ADP-ribose) polymerase inhibitors attenuates the severity of acute pancreatitis and associated liver and lung injury

BACKGROUND AND PURPOSE

The mortality associated with acute pancreatitis (AP) is largely attributable to abnormalities that occur in distant organs and supportive care remains the only treatment for patients with these complications. Recently, prophylactic pharmacological blockade of poly(ADP-ribose) polymerase (PARP) enzymes has been shown to attenuate the severity of the disease. However, the clinical relevance of PARP inhibitors administered after the onset of AP remains uncertain. The aim of the present study was to investigate the therapeutic effects of PARP inhibitors in established AP.

EXPERIMENTAL APPROACH

Mice were fed a choline/methionine-deficient/ethionine-supplemented (CMDE) diet to induce AP. PARP inhibitors were given at 36 h after the onset of CMDE diet. Severity of pancreatitis was assessed by measurements of serum amylase, lipase, IL-1beta and IL-6, and histological grading. Serum hepatic enzymes, myeloperoxidase (MPO) activity and morphological changes were measured as indicators of hepatic insult. Lung injury was evaluated by MPO activity and morphological changes. Survival rates of mice were monitored for 7 days.

KEY RESULTS

CMDE diet administration resulted in a significant increase in serum amylase, lipase, IL-1beta, IL-6, alanine aminotransferase and aspartate aminotranferase levels, indicating AP and associated liver injury. Analysis of the histopathological changes in pancreas, liver and lung revealed extensive tissue damage. Treatment of mice with PARP-inhibitors after the onset of AP was associated with a reduction in the severity of AP and, accordingly, with a reduced mortality rate.

CONCLUSIONS AND IMPLICATIONS

Our results support the therapeutic application of PARP inhibitors in the treatment of established AP.

Hepatotoxin-induced hypertyrosinemia and its toxicological significance

A (1)H Nuclear Magnetic Resonance (NMR) spectroscopic investigation of the effects of single doses of four model hepatotoxins on male Sprague-Dawley rats showed that hypertyrosinemia was induced by three of the treatments (ethionine 300 mg/kg, galactosamine hydrochloride 800 mg/kg and isoniazid 400 mg/kg) but not by the fourth (thioacetamide 200 mg/kg). Concomitant histopathological and clinical chemistry analyses showed that hypertyrosinemia could occur with or without substantial hepatic damage and that substantial hepatic damage could occur without hypertyrosinemia. However, in the rats dosed with galactosamine hydrochloride, which showed highly variable amounts of liver damage at ca. 24 h after dosing, a clear relationship was found between the degree of hypertyrosinemia and the extent of the hepatic necrosis induced. In line with the cause of clinically observed Type II Tyrosinemia, we consider that the critical event in the onset of hepatotoxin-induced hypertyrosinemia is likely to be a reduction in hepatic tyrosine aminotransferase (TAT) activity. We discuss mechanisms by which TAT activity could be lost with special consideration given to pyridoxal 5'-phosphate (P5P) depletion and to the inhibition of protein synthesis. This analysis may have implications for the interpretation of clinical measures of liver status such as Fischer's ratio and the branched-chain tyrosine ratio (BTR).

New modes of data partitioning based on PARS peak alignment for improved multivariate biomarker/biopattern detection in 1H-NMR spectroscopic metabolic profiling of urine

This paper addresses the possibility of mathematically partition and process urine ¹H-NMR spectra to enhance the efficiency of the subsequent multivariate data analysis in the context of metabolic profiling of a toxicity study. We show that by processing the NMR data with the peak alignment using reduced set mapping (PARS) algorithm and the use of sparse representation of the data results in the information contained in the original NMR data being preserved with retained resolution but free of the problem of peak shifts. We can now describe a method for differential expression analysis of NMR spectra by using prior knowledge, i.e., the onset of dosing, a partitioning not possible to achieve using raw or bucketed data. In addition we also outline a scheme for soft removal of "biological noise" from the aligned data: exhaustive bio-noise subtraction (EBS). The result is a straightforward protocol for detection of peaks that appear as a consequence of the drug response. In other words, it is possible to elucidate peak origin, either from endogenous substances or from the administered drug/biomarkers. The partition of data originating from the normally regulating metabolome can, furthermore, be analyzed free of the superimposed biological noise. The proposed protocol results in enhanced interpretability of the processed data, i.e., a more refined metabolic trace, simplification of detection of consistent biomarkers, and a simplified search for metabolic end products of the administered drug.

An hypothesis for a mechanism underlying hepatotoxin-induced hypercreatinuria

As part of a wider metabonomic investigation into the early detection and discrimination of site-specific hepatotoxicity, male Sprague-Dawley rats were dosed with the model hepatotoxins allyl formate, ethionine and alpha-naphthylisothiocyanate (ANIT). Urine samples collected pre- and post-dose were examined by (1)H nuclear magnetic resonance (NMR) spectroscopy and the toxin-induced changes in urinary taurine and creatine excretion were quantified. Hypertaurinuria and hypercreatinuria were observed following allyl formate dosing, hypertaurinuria with no change in creatine excretion was observed after ethionine dosing, and hypotaurinuria and hypercreatinuria were observed after ANIT dosing. These changes are indicative of different effects on liver and it has been previously suggested that some hepatotoxin-induced changes in urinary taurine excretion may be due to altered hepatic cysteine utilisation. A related hypothesis is now presented that would explain the selective hypercreatinuria in terms of increased cysteine synthesis.

Triglyceride disposition in isolated hepatocytes after treatment with hydrazine

Treatment of animals with hydrazine causes the accumulation of triglycerides in the liver but the mechanism remains unclear. Therefore, the effect of hydrazine on hepatic triglyceride synthesis and subsequent transport was studied in a hepatocyte model, in vitro in order to isolate liver cells from extrahepatic influences. Hepatocytes were isolated and either incubated in suspension with [14C]palmitate in the presence of hydrazine (2-12 mM) or pre-incubated with [14C]palmitate, washed free of the fatty acid and then incubated with hydrazine (2-12 mM). Hydrazine resulted in a significant reduction in the incorporation of [14C]palmitate into triglycerides and reduction in the transportation of triglycerides out of cells. When [14C]palmitate was in the incubation medium, ATP levels were reduced by lower concentrations of hydrazine than have previously been reported. None of the concentrations of hydrazine used affected cell membrane integrity (viability) as measured by LDH leakage. The 14CO2 produced by the beta-oxidation of [14C]palmitate was also measured in short term incubations (30 min) carried out in sealed vessels. There was a dose dependent increase in 14CO2 produced by very low concentrations of hydrazine (0.01-0.1 mM) after which the effect was maximal and concentrations above 8 mM hydrazine decreased 14CO2 production. The data suggest that the inhibition of transportation of triglycerides out of cells by hydrazine may have a more important role in the accumulation of triglycerides in the liver than has been previously recognised. However, the model was not able to mimic the accumulation of triglycerides in hepatocytes seen in vivo.

Pancreatic exocrine secretion is blocked by inhibitors of methylation

A number of early experiments suggested a relationship between methyl group metabolism and the exocrine secretion of the pancreas. These included nutritional studies showing that ethionine, the ethyl analog of methionine which inhibits cellular methylation reactions, is a specific pancreatic toxin. Other studies indicated that protein carboxymethylation might be involved. We now show that in vivo ethionine inhibits amylase secretion from freshly isolated rat pancreatic acini, while in vitro ethionine inhibits amylase secretion from the AR42J pancreatic cell line. S-Adenosylhomocysteine (SAH) is a product inhibitor of all methyltransferase reactions involving S-adenosylmethionine (SAM), and treatments that elevate cellular levels of SAH such as inhibition of S-adenosylhomocysteine hydrolase and the in vitro addition of adenosine and homocysteine result in the inhibition of amylase secretion in both isolated pancreatic acini and AR42J cells. Measurement of SAM and SAH levels in AR42J cells shows that inhibition of secretion is more closely related to elevation of SAH levels than to a decrease in the SAM/SAH ratio. Small G-proteins are carboxymethylated on the C-terminal prenylated cysteine and inhibitors of membrane-associated prenylcysteine methyltransferase, N-acetylfarnesylcysteine, N-acetylgeranylgeranylcysteine, and farnesylthioacetic acid (FTA), block secretion in AR42J cells. N-Acetylgeranylcysteine is not an inhibitor of the methyltransferase and does not inhibit amylase secretion. FTA inhibits membrane-associated prenylcysteine methyltransferase from AR42J cells with a Ki in the 45-69 microm range. These results suggest that a methylation event is needed for pancreatic exocrine secretion which may be the reversible methylation of a G-protein involved in signal transduction or membrane trafficking.

Influence of dietary soybean trypsin inhibitors and DL-ethionine on sulfur amino acid adequacy of diets for young rats

Weanling male Wistar rats were fed 20% protein diets based on casein or either of two combinations of soy protein isolate and ground raw soy providing three levels of soybean trypsin inhibitors (SBTI; 0, 448 and 808 mg of trypsin inhibited per 100 g of diet respectively). DL-ethionine was included at three levels (0, 0.05% and 0.10%) with each level of SBTI. After 4, 8 and 12 weeks of ad libitum feeding, diets containing SBTI without DL-ethionine were associated with decreases in weight gain, feed efficiency, serum cholesterol and serum urea nitrogen. Higher levels of triglycerides, glutamate pyruvate transaminase (SGPT) and altered serum free amino acid levels were also found. Increased dietary levels of DL-ethionine also resulted in deficits in growth and feed efficiency, decreased serum cholesterol, increased SGPT and similar alterations in serum free amino acids. Combination of dietary SBTI with DL-ethionine resulted in even greater growth deficits and serum cholesterol decreases as well as increases in SGPT and serum triglycerides and changes in serum free amino acid levels. Methionine deficiency in the young rats fed SBTI and DL-ethionine was indicated by the changes in serum amino acids and growth deficits. Moderation of some effects over the 12 week test period suggested decreased methionine requirements in the older rats.

Inhibition of the initiation of hepatic protein synthesis during ethionine mediated ATP depletion in vivo: modification to ribosomal subunits, evidence of impaired ternary complex formation and a subcellular redistribution of eIF-2 alpha

Acute ethionine intoxication is known to induce a reversible hepatic injury in female rats by reducing the level of hepatic ATP. The injury indirectly impairs the initiation of hepatic protein synthesis, with resultant polysome disaggregation. Administration of adenine rapidly restores the ATP levels and protein synthesis. Analysis of liver polysome and ribosomal subunits reveals that polysome disaggregation occurs following 3 h of the intoxication, and reaggregation occurs following the administration of adenine. Inactive hepatic ribosomes accumulate as monomers and disomes when analysed by sucrose gradient sedimentation in low-salt buffers. High-salt buffers dissociate the inactive ribosomes into the component 40 S and 60 S subunits. The level of higher density, 1.48 g/cc, 40 S subunit increases during the inhibition of protein synthesis, while the lower density, 1.41 g/cc, 40 S subunit species does not change significantly. Hepatic microsomal and cytosolic extracts examined for their ability to support the formation of the ternary complex of eIF-2-GTP and [35S]Met-tRNAi demonstrate that during acute ethionine intoxication, ternary complex formation in the two extracts decrease 65% and 85%, respectively. These changes are coincident with polysome disaggregation. Administration of adenine to reverse the intoxication restores the ternary complex forming ability of the cytosolic extract, but does not affect the activity of the microsomal salt wash extracts. Mixing experiments indicate the accumulation of an inhibitor of ternary complex formation in the microsomal salt wash fraction. The application of quantitative western blotting demonstrates that the level of antigenic eIF-2 alpha in the microsomal salt wash extract increases 31% during the inhibition. These observations are consistent with the idea that the inhibition of the initiation of hepatic protein synthesis induced by ethionine is mediated by eIF-2 alpha phosphorylation. The latter results in an inhibition of ternary complex formation, redistribution of eIF-2 to the microsome fraction, polysomal disaggregation, and accumulation of inactive ribosomal subunits.

Course of ATP depletion in hydrazine hepatotoxicity

The effect of hydrazine on ATP levels has been investigated in rats in vivo and in hepatocytes in vitro. Hydrazine was found to cause a dose-dependent depletion of hepatic ATP in vivo 3 h after dosing. In isolated hepatocytes in vitro hydrazine also caused a concentration-dependent depletion of ATP which preceded cytotoxicity as indicated by loss of cell viability. The ATP depletion in isolated hepatocytes was also significant at a concentration of hydrazine which was not cytotoxic. Attempts to determine hepatic ATP depletion in vivo over time using topical 31P NMR were confounded by the effects of the thiopentobarbitone used to anaesthetise the animals. This was found to ameliorate the effects of hydrazine on ATP depletion but potentiate the lethality of hydrazine. Consequently, although ATP depletion was detected in some hydrazine-treated animals, this was only observed in animals which subsequently died. The results indicate that ATP depletion may underlie the hepatotoxicity of hydrazine.

Reduced binding and removal of chylomicron remnants by ethionine-induced premalignant liver

The suppression of cholesterol synthesis by dietary cholesterol which occurs in the livers of normal animals is absent in hepatomas. This abnormality has been reported to occur in the livers of animals fed hepatocarcinogens, even before there is any histologic evidence of malignancy (premalignant liver). We have proposed, in an earlier publication, that the deletion of feedback inhibition of cholesterol synthesis in malignancy is due, at least in part, to the loss of receptors which bind chylomicron remnants, the lipoprotein particles that transport dietary cholesterol to the liver. This hypothesis was further tested in the premalignant liver model. Rats were fed a diet containing 0.25% of a known hepatic carcinogen, ethionine. After 3 to 5 weeks on this diet, the liver had no histologic evidence of malignancy; the rate of [14C]acetate incorporation into cholesterol by liver homogenates was elevated as compared to that of controls (5.13 +/- 0.70 vs. 0.65 +/- 0.14 nmoles cholesterol per gm per hr), and in contrast to control animals, this was not reduced by the inclusion of 5% cholesterol in the diet for 48 hr before killing. The serum (44.4 +/- 6.3 vs. 51.4 +/- 3.8 mg per 100 ml) and hepatic (15.8 +/- 0.2 vs. 17.0 +/- 0.4 micrograms per mg protein) cholesterol contents were not substantially different in ethionine-fed as compared to control-fed rats. Hepatic cholesterol content increased when cholesterol was included in the diet (15.8 +/- 0.2 to 25.8 +/- 7.3 micrograms per mg protein and 17.0 +/- 0.4 to 36 +/- 3.7 micrograms per mg protein in ethionine-fed and control-fed animals, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear magnetic resonance spectroscopy and imaging in the study of experimental liver diseases

We are investigating potential noninvasive new strategies for the assessment of liver injury, steatosis, and hepatic tumor development. These techniques employ nuclear magnetic resonance (NMR) imaging and spectroscopy. Accordingly, several experimental animal models of liver injury and steatosis produced in rats by ethanol, azaserine, L-ethionine, carbon tetrachloride, and D-galactosamine. Ethanol and L-ethionine induce acute steatosis without necrosis, whereas azaserine, carbon tetrachloride, and D-galactosamine are known to produce steatosis with varying degrees of hepatic necrosis. Triglyceride content and protein spin relaxation times were measured. T1 values were analyzed by using an inversion recovery technique at eight different tau values (20 msec to 2.50 sec) and T2 by Carr-Purcell-Meibloom-Gill pulse sequences with 10 spin echoes (4-40 msec). We also performed NMR imaging studies on controls and ethanol-induced steatosis using a 60-MHz Technicare 8-cm bore superconducting system. Results of these experiments indicate that varying degrees of steatosis produce striking changes in T2 without inducing changes in T1, whereas necrosis superimposed on steatosis produces T1 changes as well. Thus, these NMR spectroscopy and imaging studies demonstrated that steatosis may be clearly defined in vitro and in vivo.

Rapid changes in glucose metabolism following the administration of ethionine: its role in regulating hepatic protein synthesis

The relationship between the changes in portal glucagon, insulin, glucose, and hepatic protein synthesis were investigated during ethionine intoxication. There was a 50% decrease in blood glucose, a seven-fold increase in portal glucagon and a 90% increase in portal insulin, all of which coincided temporally with the inhibition of hepatic protein synthesis. When reversal of ethionine intoxication was initiated with adenine it simultaneously restored blood glucose, insulin, glucagon, and protein synthesis. Protein synthesis could not be adequately restored by glucose, but in this case hepatic ATP levels did not increase. In addition, glucose given by stomach tube prior to ethionine did not prevent the action of ethionine, though it did maintain plasma glucose levels and prevented the decrease in plasma insulin and increase in plasma glucagon. These results show that in vivo regulation of hepatic protein synthesis during ethionine intoxication is not likely to be mediated by portal insulin, glucose, and glucagon.

Hg- and Cu-induced hepatocellular changes in the mummichog, Fundulus heteroclitus

To investigate mechanisms by which the mummichog (F. heteroclitus) successfully withstands heavy metal pollution, fish were treated with Hg2+ at up to 0.10 mg/L, Cu2+ at up to 1.0 mg/L, or combinations of Hg2+ and Cu2+. In earlier work, protein analysis of liver indicated that most of the cytosolic Cu is bound to the sulfhydryl-rich metallothionein, but that Hg is not associated with cytosolic proteins. Morphometric analysis indicates the Hg-treatment increases the lipid compartment of hepatocytes (ANOVA, F = 10.73, p less than 0.01). This lipid increase is correlated with the Hg content (analyzed by atomic absorption spectrophotometry) of individual liver samples (Spearman rank correlation, rs = 0.621, p less than 0.01). Cu treatment causes a reduction in the lipid compartment (F = 10.38, p less than 0.01), reduced cytoplasm in general (F = 18.55, p less than 0.001) and an increased lysosome count (F = 14.21, p less than 0.001). X-Ray microanalysis locates Cu in secondary lysosomes, but not in other organelles. Results of treatment with both Hg2+ and Cu2+ are similar to those of Hg2+ alone. Concentrations of Cu in liver varied too much to allow assessment of correlations with cytoplasmic changes. Usual mechanisms for handling toxic heavy metals include binding to metallothionein and sequestering in lysosomes. Our findings for Cu are in agreement with this. Fish, however, can methylate Hg. (We have found greater than 75% of killifish hepatic Hg to be methylated.) Increased cellular lipid may be a mechanism for sequestering the lipid-soluble methylmercury.

Ethionine in the analysis of the possible separate roles of methionine and choline deficiencies in carcinogenesis

The importance of ethionine, the ethyl analogue of methionine, as a metabolic probe to study the possible roles of methionine and choline in liver carcinogenesis has been briefly reviewed. Ethionine-induced liver carcinogenesis is similar in many aspects, including initiation, promotion, and progression, to carcinogenesis with other agents. However, the special role of methionine in preventing virtually all metabolic and pathologic effects of ethionine, including liver cancer, places ethionine in a special position. On the basis of these observations and our current knowledge about choline deficiency in the genesis of liver cancer, we proposed that choline and methionine play separate but overlapping roles in the initiation and promotion of liver carcinogenesis.

Coupling of ATP synthesis to reversal of rat liver microsomal Ca2+-ATPase

The reversal of the rat liver microsomal Ca2+-ATPase transport cycle was studied. Microsomes were loaded with 45Ca2+ (approximately 30 nmol/mg of protein) in an ATP-dependent process, and the time dependency of the microsomal 45Ca2+ efflux was determined with various ADP and inorganic phosphate (Pi) concentrations. Pseudo-first-order rate constants (K'e) for 45Ca2+ efflux were determined. Although there was considerable 45Ca2+ efflux in the absence of added ADP or Pi, the addition of ADP or Pi alone had minimal effects upon the K'e; in contrast, a 2.5-fold increase in the K'e was observed in the presence of both ADP and Pi. The apparent Km values for ADP and Pi were 4 microM and 0.22 mM, respectively. Stimulation of 45Ca2+ efflux by ADP and Pi was associated with ATP synthesis. The calcium ionophore A23187 prevented ATP synthesis, which indicates that the Ca2+ gradient facilitates the coupling of ATP synthesis to Ca2+ efflux.

Cyclic AMP binding activity in liver supernatants during acute ethionine intoxication

There is a significant increase in hepatic cAMP binding activity 4 hr following ethionine intoxication. This activity is localized to the 100, 000 g supernatant. The binding of cAMP by the 100, 000 g supernatant of controls can be increased to experimental levels simply by dialysis. The increased binding activity seen during ethionine intoxication can be reversed by the administration of adenine. Neither S-adenosyl ethionine, S-adenosyl methionine, S-adenosyl homocysteine, nor AMP compete effectively with cAMP for the binding protein. Increasing ADP concentrations stimulates cAMP binding whereas increasing ATP concentration inhibits cAMP binding. At concentrations seen during ethionine intoxication the effects of ADP and ATP were equal but opposite in direction.

Hepatic adenylate cyclase and phosphodiesterase activity during acute ethionine intoxication

Four hours after the administration of ethionine and in the face of an 80-90% depletion of hepatic ATP there is a twofold increase in cAMP. This increase in cAMP is shown not to be effected by a reduction in phosphodiesterase activity. Both the low Km and high Km forms of the enzyme retain their activity. The purification of liver plasma membranes is not affected by ethionine. There is a significant 20% increase in plasma membrane adenylate cyclase activity following acute ethionine intoxication. This was demonstrable using either ATP or 5'-adenylyl-imidodiphosphate as substrates. The plasma membranes, isolated in the presence of Ca2+, have a 20-fold higher basal adenylate cyclase activity then previously reported and are not further stimulated by GTP or NaF. A modified protocol for isolating cAMP from the adenylate cyclase reaction is described.

The acute toxicity of oxamniquine in rats; a sex-dependent hepatotoxicity

Toxicity studies with oxamniquine in several laboratory animal species revealed an idiosyncratic sensitivity of rats, females being much more sensitive than males. After single p.o. doses of oxamniquine, rats died up to 14 days after the dose from hepatic failure. At doses near the LD-50, serum transaminases were high and proteins low from 24 h after the dose in females and from 48 h in males; serum and liver triglycerides showed no clear changes. Histologically the livers were characterised by cytoplasmic inclusion bodies, parenchymal necrosis, and bile duct proliferation. Metabolism and pharmacokinetic data were inadequate to explain the sex-dependency of this toxicity, but tissue distribution studies with carbon-14 labelled oxamniquine showed that 72 h after a given dose livers of female rats retained more label than males, and that little of this was due to unchanged drug.

Ultrastructural alterations of the liver of Pekin ducks fed methyl mercury-containing diets

This report describes the ultrastructural alterations of the liver of 24 male and 24 female Pekin ducks fed 0.0, 0.5, 5.0, and 15.0 ppm of methyl mercury chloride (MeHgCl), mixed in a mash diet, for 12 wk. Birds were weighed weekly and observed for neurologic symptoms daily. Samples of blood, liver, kidney, skeletal muscle and brain were analyzed for Hg residue by atomic absorption spectrophotometry. Livers were fixed in situ by perfusion with glutaraldehyde fixative and processed for electron microscopy. The percent decreases in mean body weights between wk 0 and wk 7 were statistically not significant except for males fed 5.0 ppm MeHgCl. Leg paralysis and convulsions in males treated with 15.0 ppm began at wk 5 and in females at wk 8, but were more severe in the latter. The dose-residue response for the three dose levels in all five tissues was linear, with liver and kidney containing the highest and the brain the least amount of Hg. Hepatocytes in 0.5- and 5.0-ppm MeHgCl treatment groups showed little morphologic changes, while liver cells in the 15.0-ppm group had several ultrastructural alterations, including remarkable increase in peribiliary lysosomal bodies. The mitochondria of some hepatocytes exhibited lysis of both inner and outer membranes. Changes also occurred in endothelial and Kupffer cells. These results indicate that dosing Pekin ducks with 15.0 ppm causes ultrastructural alterations indicative of toxic injury to the liver.

Valproate-induced hepatic steatogenesis in rats

The administration of high-dose valproic acid (VPA) (750 mg per kg) consistently produced significant microvesicular steatosis in mature Sprague-Dawley rats after 48 hr. Similar changes occurred in animals pretreated with phenobarbital which received a lower dose of VPA (350 mg per kg), but no steatosis was seen in animals treated with the low-dose VPA alone. The steatogenic effect of VPA is most likely mediated by a toxic metabolite. It can also be speculated that phenobarbital, by enhancing the inducing effects of the hepatic mixed-function oxidase system, may lead to increased conversion of VPA to a toxic metabolite. Young and weanling rats appeared to be resistant to the steatogenic effects of VPA. Reproduction of microvesicular steatosis in this experimental; model may permit exploration of factors that enhance or inhibit VPA-induced hepatic injury.

Alterations in the enzyme activity and polypeptide composition of rat hepatic endoplasmic reticulum during acute exposure to 2-acetylaminofluorene

Studies have been made of the morphology, enzyme activity and protein composition of liver endoplasmic reticulum in rats exposed to acute doses of the carcinogen, 2-acetylaminofluorene (2-AAF). Electron microscopic examination revealed numerous ultrastructural changes in the hepatocyte; most consistent alterations were the disorganisation of endoplasmic reticulum system with apparent increase of smooth endoplasmic reticulum. Administration of 2-AAF to rats immediately depressed microsomal glucose-6-phosphatase activity and eventually induced epoxide hydratase activity 6--7-fold over control activity. The induction was time-dependent and maximal rates of induction were observed at dosages greater than 40 mg/kg body wt. The treatment also induced cytochrome b5 content, NADH and NADPH cytochrome c reductase activities (1.0--1.5-fold). Only very small changes in the total content of cytochrome P-45- were noted. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of microsomal proteins from 2-AAF pretreated animals showed time-dependent induction of two polypeptides which differed slightly in migration, in the region of Mr = 48000; the fast-migrating induced polypeptide has been identified as epoxide hydratase. Two-dimensional PAGE analysis of microsomal proteins from 2-AAF exposed rats showed a reproducible deletion of a protein with molecular weight in the region of 67000. The basis for the alterations in the protein composition of endoplasmic reticulum in response to 2-AAF treatment is discussed.

NADP-dependent dehydrogenases in rat liver parenchyma. III. The description of a liponeogenic area on the basis of histochemically demonstrated enzyme activities and the neutral fat content during fasting and refeeding

The activities of glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase(6PGDH), malic enzyme (ME) and isocitrate dehydrogenase (ICDh) were investigated with optimized histochemical methods (Rieder it al 1978), and the activity of 3-hydroxybutyrate dehydrogenase (3HBDH) and neutral fat content with conventional techniques in the liver of male rats under the following experimental dietary conditions: (A) Fasting for 0, 12 and 84h; (B) 84-h fasting followed by refeeding with a low-fat, high-carbohydrate diet for 6 h and for 2, 3, 5, 7, 11 and 14 nights; (C) refeeding with standard diet for 5 nights; (D) low-fat high-carbohydrate diet for 7 an 14 nights. The activities of G6PDH, 6PGDH and ME decreased slightly during fasting primarily in zone 1 and increased dramatically on refeeding with a low-fat, high-carbohydrate diet. This activity increase was confined mainly to zone 3 during the first 3 days and was accompanied by a deposition of neutral fats that began in zone 3 and progressed to zone 1. Neutral for accumulation was maximal after 3 nights, with a uniform accumulation of large droplets in all the hepatocytes; this was followed by a release that started in zone 3 and proceeded in a periportal direction. On the other hand, G6PDH, 6PGDH and ME attained their maximum activities after 5 amd 7 nights of low-fat diet, the activities being nearly homogeneously distributed over the liver acinus in a few cases. Subsequently the activities fill mainly in zone 1, causing the activity patterns and levels to approach those of the animals in group (D). In contrast to this, the activity of ICDH increased during fasting principally in zone 1, so that the otherwise steep activity gradient in favor of zone 3 lessened. Refeeding led at first to a fall of activity below the initial value, but later the normal distribution pattern was restored. The activity of 3HBDH showed a behavior similar to that of ICDH. The findings are discussed with reference to the functional heterogeneity of the liver parenchyma, and the existence of a liponeogenic area in zone 3 is proposed.

Liver and serum lipids and lipoproteins of rats fed 5% L-lysine

Soybean protein and casein supplemented with 1% Arg were compared for their ability to prevent fatty livers caused by excess dietary Lys. The concentrations of serum lipids and lipoproteins of rats fed 5% Lys and having vatty livers were also compared with those of rats fed the identical diet but lacking fatty livers when killed. The total liver lipids, triglycerides and cholesterol of rats fed 15% casein +5% Lys were 3.9, 12.4 and 2 times control values, respectively. Rats fed 5% Lys +1% Arg or 5% Lys with 15% soybean protein had liver lipid concentrations similar to controls fed no supplemental Lys. Serum total lipids, triglycerides, cholesterol, phospholipids and free fatty acids also did not change, and serum ketone bodies were slightly elevated with Lys feeding whether the rats had fatty livers or not. The concentrations of circulating HDL were slightly depressed in all rats fed 5% Lys while LDL were significantly elevated, particularly in rats without fatty livers. Serum VLDL did not change with 5% dietary Lys. Overall, excessive dietary Lys caused fatty livers which were prevented by varying the diet or length of feeding. Excess Lys feeding altered lipoprotein metabolism shown by decreased serum HDL and a substantial elevation in LDL. The latter was more apparent when the fat accumulation in liver was less severe or absent. The data suggest that the fatty liver from Lys excess is probably unrelated to increased fat mobilization from storage, decreased fat oxidation or to a major block in the transport of triglycerides from the liver to the circulation.

Metabolism of toxic substances in isolated hepatocytes

Chloroform and selenite toxicity have been studied in isolated hepatocytes. Two different toxic mechanisms, which lead to cellular lysis after distinct lag periods, are compared. Chloroform toxicity can be divided into 2 phases, a first phase characterized by chloroform metabolism and a second phase characterized by lipid peroxidation. GSH depletion during the first phase is claimed to be a prerequisite for lipid peroxidation in the second phase. Selenite metabolism leads to cofactor depletion as well. Selenite reduction via a GSH reductase dependent pathway exhausts the cells of NADPH and this effect can be related to cellular lysis.

Influence of 4-aminopyrazolopyrimidine on morphology, synthesis of triglyceride and protein and their secretion in rat hepatocytes

The influence of 4-aminopyrazolopyrimidine (4-APP) on morphology and on synthesis and secretion ability of isolated rat hepatocytes was investigated: 4-APP was found to inhibit both the synthesis and secretion of proteins. The synthesis of triglycerides was unaffected by 4-APP, while the secretion of triglycerides was markedly reduced. Transmission electron microscopy revealed that 4-APP induced morphological changes in the smooth membrane systems, the smooth endoplasmic reticulum and the Golgi apparatus. The possibility that 4-APP inhibits lipoprotein formation by inhibition of the apoprotein synthesis is discussed.

Fatty liver in hypervitaminosis A: synthesis and release of hepatic triglycerides

Feeding large doses (30,000 IU/100 g body wt per day) of vitamin A to young rats for 2 days produced fatty liver, caused a stimulation of oxidation and esterification of [1-14C]palmitate by liver slices, and increased the activity of hepatic palmitoyl-CoA synthetase. Under similar conditions, however, release of hepatic triglycerides into the plasma, as judged from the post-Triton triglyceridemia, remained unaffected. It is indicated by the present findings that excessive intake of vitamin A produces fatty liver by stimulating the synthesis of triglycerides in liver without affecting the rate of secretion of hepatic triglycerides. An involvement of altered oxidation of fatty acids in the liver can also be ruled out because in hypervitaminosis A this process is increased rather than decreased as required for fatty liver production.

Loss of the lipoprotein lipase activating ability of rat serum after administration of some fatty liver inducing drugs

The effects of the administration of different fatty liver inducing drugs on the serum lipoprotein lipase activating ability was investigated in rats. Addition of serum from 2-mercaptoethanol-, 2-mercaptoacetate-, ethionine- or D-galactosamine- treated rats failed to activate heart and adipose tissue lipoprotein lipase from control rats. The activating effect of serum was only slightly reduced in isopropanol-treated rats, whereas it was found unaffected in ethanol-treated ones. Electrophoresis of the lipoproteins and of the very low density lipoproteins (VLDL) fraction of sera from 2-mercaptoethanol-, 2-mercaptoacetate-, isopropanol-, ethionine- and D-galactosamine-treated rats suggest that the lack of lipoprotein lipase activation ability of these sera is most probably related to the impairing effects of these drugs upon VLDL metabolism, i.e. reduction of VLDL secretion in the case of 2-mercaptoethanol, 2-mercaptoacetate and isopropanol, production of abnormal VLDL in the case of D-galactosamine and both decreased VLDL secretion and production of abnormal VLDL in the case of ethionine.

Effect of dietary DL-ethionine on growth and liver metabolism

The effects of DL-ethionine, given in the diet or by injection, on growth, hepatic glycogen and lipids, and the activities of some cytoplasmic NAD-linked dehydrogenases and NADPH-producing enzymes were investigated. 2. Growth virtually ceased after feeding ethionine for 2 d. 3. Ethionine induced an accumulation of lipid, decreased the activities of malic enzyme and isocitrate dehydrogenase and increased the activity of lactate dehydrogenase. 4. The concentration of glycogen in the liver of ethionine-fed chickens increased for 3 d in spite of a decrease in food intake, but then decreased.

Reversal of ethionine intoxication in the domestic fowl with methionine and adenine sulphate

When DL-methionine was administered to young chickens fed on a diet containing DL-ethionine (2 g/kg) growth recommenced and proceeded linearly for the first 2 d; the rate was dependent on the amount of methionine administered. 2. Adenine sulphate did not stimulate growth but when given with methionine the response was enhanced.

Effects of reduced ATP concent on hepatic responses to glucagon

Expression of the glycogenolytic action of glucagon in liver requires ATP for cAMP formation and for several subsequent phosphorylation reactions. To assess the extent to which ATP availability is rate-limiting to this hormonal action, responses to glucagon of intact liver and of liver with marked reductions in ATP content induced by ethionine was examined in female Wistar rats in vivo and in vitro. Compared to values in quick-frozen liver samples from control rats, basal hepatic ATP was 75% lower and cAMP, two fold higher in rats treated with ethionine. Activation of glycogen phosphorylase and inactivation of glycogen synthetase, phosphorylation reactions which require ATP and are initiated by cAMP, were also evident in basal liver samples from ethionine-treated rats. These hepatic alterations were associated with portal glucose and insulin levels which were significantly lower and portal glucagon levels which were four fold higher than values in controls. In ethionine-treated rats, glucose infusion decreased hepatic cAMP content and phosphorylase activity and increased synthetase activity. This and other observation suggested that the higher cAMP and the altered enzyme activities seen in vivo after ethionine administration were mediated by the hyperglucagonemia and/or by other endogenous glycogenolytic stimuli, and accordingly implied that liver remained responsive to such stimuli despite reduced ATP. Pharmacologic doses of exogenous glucagon clearly increased cAMP in vivo and in vitro in livers with decreased ATP. However, the lower ATP of liver exposed to ethionine was associated with a significantly blunted cAMP response to maximal glucagon stimulation. By contrast, alterations in phosphorylase and synthetase activities were not similarly blunted, suggesting that the smaller increases in cAMP seen in liver with reduced ATP content were adequate for the expression of these actions of the hormone. It is concluded that the actions of glucagon to increase cAMP and to activate phosphorylase and inactivate synthetase are not abolished by marked reductions in hepatic APT.